Devel of bone

Question 1

Development of bones is different based on?

Answer 1

calcification

Question 2

all bones derive from mesenchyme (embryonic connective tissue) via?

Answer 2

2 different processes:

1) intramembranous ossification
2) endochondral ossification

Question 3

Bones made by intramembranous ossification

Answer 3

Flat bones of the skull, Mandible, Clavicle

Question 4

Membranous bone formation means?

Answer 4

mesenchymal models of bones form in the embryo, the direct ossification of the mesenchyme begins (during the fetal period).

Question 5

Intramembranous Ossification Steps

Answer 5

1) Beginning in week 8 of embryonic development, some mesenchymal cells migrate to form aggregations called ossification centers
2) Mesenchymal cells differentiate into osteoblasts, which can produce bone matrix to be calcified. Once encased in bone, the osteoblasts become osteocytes
3) Bone growth in linear extensions (spicules). Angiogenesis occurs.
4) Enlargement and fusion of spicules into woven network of ‘spongy bone’. appositional growth – increase in diameter of bone

Question 6

In contrast, endochondral ossification occurs?

Answer 6

where a cartilage precursor served as a model for bone formation

Question 7

Bones developed by endochondral ossification

Answer 7

Bones of extremities, Vertebrae, Cranial base

Question 8

Diaphysis

Answer 8

shaft, compact bone with medullary cavity filled mainly with yellow marrow.

Question 9

Epiphysis

Answer 9

ends of bone, mostly spongy and containing red marrow

Question 10

Epiphyseal line

Answer 10

growth plate

Question 11

Endochondral Ossification Steps

Answer 11

1) Intramembranous ossification begins with mesenchymal cells differentiate into chondroblasts (the cartilage-producing cells), which produce cartilage matrix. This creates a hyaline cartilage model of the shape of the ‘future’ bone.
2) Bone cuff (collar) develops in midregion of cartilage. What was the perichondrium coverts into periosteum, producing osteoblasts. The chondrocytes in the center of the cartilage enlarge and the cartilage matrix calcifies. Chondrocytes then die, producing cavity.
3) Blood vessels grow around cartilage
and bony collar, and some penetrate
through to the cavity, taking osteoprogenitor cells into the matrix. This forms a primary ossification center.
4) Bone formation ‘spreads’ along shaft toward both ends, and remodeling continues creating a marrow cavity. Growth occurs by both interstitial (length) and appositional (diameter) growth.
5) Secondary ossification centers develop in the epiphyses. Eventually, the only cartilage remaining is articular cartilage on the surface and a thin plate, called the epiphyseal plate, between the bone of the epiphyses and diaphysis.
6) Growth in the length of the bone occurs at the epiphyseal plate, as long as the rate of cartilage production = bone production/cartilage replacement. In a mature bone, the epiphyseal plate is replaced by an epiphyseal line.

Question 12

the cranial base also undergoes growth via? How?

Answer 12

endochondral ossification! By synchondroses!

Question 13

Cranial synchondroses is?

Answer 13

cartilaginous joints of the base of the
skull. These synchondroses act as
growth centers until puberty, when they begin to ossify – calcification is usually complete around 25 yrs.

Question 14

Cranial synchondroses examples?

Answer 14

-spheno-occipital (sphenobasilar)
synchondrosis
-sphenoethmoidal synchondrosis

Question 15

appositional verses interstitial growth?

Answer 15

apositional= diameter
interstitial= length